Upstream and downstream (transduction)

In molecular biology, the terms upstream and downstream can refer to the temporal and mechanistic order of cellular and molecular events. For example, in signal transduction, the second messenger acts downstream to – that is to say, temporally after – activation of cell membrane receptors. The other way around, activation of cell membrane receptors occurs upstream of – that is to say, prior to – the production of second messengers. In molecular biology, the terms upstream and downstream can refer to the temporal and mechanistic order of cellular and molecular events. For example, in signal transduction, the second messenger acts downstream to – that is to say, temporally after – activation of cell membrane receptors. The other way around, activation of cell membrane receptors occurs upstream of – that is to say, prior to – the production of second messengers.